Method of producing porous hollow nickel bodies



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3,371,405 Patented Mar. 5., 1968 3,371,405 METHOD OF PRODUCING PORDUS HOLLOW NICKEL BODIES Allen L. Klibanoir, Boston, Mass, assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed Dec. 23, 1964, Ser. No. 420,843 1 Claim. (Cl. 29-423) ABSTRACT OF THE DISCLOSURE A method of producing hollow nickel bodies having a uniform wall thickness comprising non-electrolytically plating a layer of porous nickel on the surface of a polystyrene substrate and thereafter leaching the polystyrene substrate from the plated substrate.

It has been proposed to utilize seamless light weight hollow metallic spheres, having uniform thicknesses, as compressible bodies for registering the effects of pressure caused by explosive systems. In such use the spheres would need to have a high degree of dimensional uniformity and compositional purity in order that a basis for forming a comparative analysis of pressure effects between different devices which are to be tested. Prior art methods of producing such hollow spherical bodies such as casting, injection moulding etc. do not produce bodies having the desired high degree of uniformity that is required in such a testing program.

It is an object of this invention to provide those skilled in the art with a novel and efficient method of producing seamless hollow metallic bodies having a high degree of dimensional uniformity and purity of composition.

This and other objects of this invention will in part be obvious and will in part appear hereinafter.

In accordance with the present invention, seamless hollow porous nickel bodies having a uniform wall thickness can readily be produced by non-electrolytically plating a uniform coating of porous nickel over the entire external surface of a polystyrene substrate; contacting the plated body with trichloroethylene until the polystyrene substrate has been substantially leached out of the plated body.

Non-electrolytic nickel plating system (sometimes referred to in the art as electroless nickel plating systems) for plating non-metallic substrates are well known to those skilled in the art. The non-electrolytic nickel plating systems found useful in the practice of this invention generally employ a chemical reducing agent such as so dium hypophosphite to reduce a nickel salt such as nickel chloride in hot aqueous solution and to deposit nickel on a catalytically activated substrate. The deposits from such systems are nickel phosphorous alloys containing from about 4 to about 12 percent phosphorus. Because the plating in such systems is not dependent on current distribution it is uniform in thickness, regardless of the shape or size of the plated surface.

NiSOi NaHzPOg H2O Ni NaHzPOa :l: HZSO-l Catalyst The essential requirements for any electroless nickel solutions are:

( l) A salt to supply the nickel (2) A hypophosphite salt to provide chemical reduction (3) Water (4) A complexing agent (5) A bulfer to control pH (6) Heat (7) A catalytic surface to be plated.

Detailed discussions of the chemical characteristics of electroless baths are well known to those skilled in the art.

Nickel and hypophosphite ions can exist together in a dilute solution without interaction, but will react on a catalytic surface to form a deposit. Furthermore, the surface of the deposit is also catalytic to the reaction so that the catalytic process continues until any reasonable plate thickness is applied.

Metals that catalyze the plating reaction are members of Group VIII in the Periodic Table, which group includes nickel, cobalt, and palladium. A deposit will begin to form on the surfaces of thesev metals by simple contact with the solution.

The external surfaces of the polystyrene bodies used in this invention are catalytically activated by the application of traces of one of these strongly catalytically active metals to the non-metallic surface of the body by mechanical or chemical means. In the preferred embodiment of this invention the surface of polystyrene bodies to be coated are catalytically activated by immersing the beads in a one percent aqueous palladium chloride solution for about minutes and-thereafter washed with distilled water to remove any excess catalyst.

Both alkaline (pH 7.5 to 10) and acid (pH 4.5 to 6) electroless nickel baths can be used in the practice of this invention.

Table I given below shows typical alkaline electroless baths which are useable in the practice of this invention:

TABLE I.ALKALINE ELECTROLESS NICKEL BATI-IS Constituent or condition Bath 1 Bath 2 Bath 3 Composition, Grams per Liter:

Nickel chloride 45 30 Operating Conditions:

pH Temperature, F Plating rate (approx.), mil per h Table II given below shows typical acid electroless baths which are useable in the practice of this invention:

TABLE II.ACID ELECTROLESS NICKEL PLATING BATHS Constitutent or condition Bath4 Bath5 Bathfi Bath7 Bath8 Bath 9 Composition, Grams per Liter:

Nickel chloride Nickel sulfate Sodium hypophosphite Sodium acet Sodium hydroxyacetat Sodium succinate Lactic acid Propionic acid Operzging Conditions:

Temperature, F

Pllzliting rate (app The follOWing example is given to illustrate the practice of this invention:

milliliters of polystyrene beads (sold by the Foster Grant Company under the trademark -T Crystal Beads AR 9100) weighing about 5 to 10 grams having an average bead diameter of 0.015 inch were immersed for minutes in a 1.0% aqueous palladium chloride solution to catalytically activate the surface of the beads. The activated beads were then rinsed with distilled water and placed in 400 ml. of an electroless plating solution. The plating solution used in this example was a commercially available nickel-phosphorous electroless plating solution sold by the Cahill Chemical Corporation of Providence, R.I., under the trademark Renidize Solution. At the time the beads were placed in the solution, the temperature of the solution was C., thereafter the temperature of the solution was raised to C. and held there for 30 minutes after the start of coating was visually observed.

The coated beads were then removed from the plating bath, rinsed in distilled water and allowed to dry.

The dried coated spheres were then placed in a vessel containing trichloroethylene and it was noted that the spheres initially floated on the surface of the trichloroethylene. As the trichloroethylene dissolved the polystyrene contained in the plated spheres, the spheres began to sink to the bottom of the vessel. After all of the spheres had sunk to the bottom of the vessel the polystyrene-containing trichloroethylene solution was decanted from the vessel and thereafter the hollow metal spheres were washed several times with trichloroethylene and allowed to dry. The dried spheres were found to have average particle diameter of 0.15 inch and an average bulk density of less than 0.005 gm./ cc.

From the foregoing example, it is obvious that the novel process disclosed in this invention provides an economical, efficient process for producing hollow seamless metal bodies. The process employs commercially available materials and can readily be scaled up to economically produce large quantities of hollow metal bodies having a high degree of dimensional uniformity. The process can be used to produce light weight decorative bodies such as statues or to produce building materials such as a metallic building material having both a series of closed voids and a series of interconnecting voids. The metal spheres produced in the example given herein could be placed in closed proximity with each other and sintered to form a building material.

What is claimed is:

1. A method for producing hollow nickel bodies having a uniform wall thickness comprising:

(a) non-electrolytically plating a uniform porous coating of nickel over the entire external surface of a polystyrene sphere having an average diameter of about 0.15 inch until a coating of nickel having an average bulk density of less than 0.005 gm./cc. is coated onto said spheres;

(b) contacting the polystyrene substrate contained in the plated sphere with trichloroethylene until the polystyrene substrate has been substantially leached out of the plated sphere through the micropores.

References Cited UNITED STATES PATENTS 3,135,044 6/1964 Mote et al. 29183 3,271,119 9/1966 Woodberry 29-191 HYLAND BIZOT, Primary Examiner.

RICHARD O. DEAN, DAVID L. RECK, Examiners. 

